The results of the DW-MRI will be compared with those of PET, CT and conventional MRI which are now routinely performed for the diagnosis of colorectal tumors. The scans will be performed in a group of patients on a 3 Tesla MR system. This system is fully approved by the European and American standards and the patients will not be exposed to radiation or contrast agents. In principle, all patients treated for gastrointestinal cancer were included after informed consent from the patient. This study is important to investigate whether DWI is accurate in the pre-therapeutic injury detection and staging of gastrointestinal tumors compared with PET / CT and DWI. In addition it is important to predict the outcome after therapy.